Color developing high impact polystyrene sheet and method of developing color images inside the same

ABSTRACT

Color images having excellent resistances to sunlight, water and rubbing are developed by bringing, in accordance with the desired pattern, an acid-reactive colorless color forming dye solution in a non-volatile organic liquid capable of dissolving or swelling polystyrene into contact with an acid color developing high impact polystyrene sheet which comprises a substrate layer consisting of a high impact polystyrene film which has been stretched in at least one direction, at least one paper-like rough surface layer provided on the substrate layer by treating the surface portion of the high impact polystyrene film with an organic liquid capable of dissolving or swelling polystyrene, and having therein numerous microvoids, and acid color developing agent for the acid-reactive colorless color forming dye, the acid color developing agent being contained in the microvoids, whereby the colorless color forming dye solution penetrates into the microvoids and forms color images inside the sheet.

Shimizu et a1.

COLOR DEVELOPING HIGH IMPACT POLYSTYRENE SHEET AND METHOD OF DEVELOPING COLOR IMAGES INSIDE THE SAME Inventors: Takuji Shimizu, Yokohama; Isao Ohara; Kenji Yasuda, both of Tokyo, all of Japan Assignee: Oji Paper Co., Ltd., Tokyo, Japan Filed: June 19, 1973 Appl. No.: 371,395

Foreign Application Priority Data June 24, 1972 Japan 47-62829 US. Cl. 428/307; 282/275; 428/212; 428/306; 428/320; 428/409; 428/910; 428/338; 428/339; 428/327; 427/151 Int. C19... B32B 3/26; B32B 5/18; B41L 1/00 Field of Search 16l/D1G. 1, 164, 162, 159;

References Cited UNITED STATES PATENTS 4/1966 Farnham et a1 117/368 X 6/1970 Tani et al 117/11 11/1970 Lin 117/368 X 1/1972 Brockett 117/362 5/1972 Miller et al. 117/368 X 8/1972 Lin 117/362 X NOV. 11, 1975 3,741,860 6/1973 Otsuho et al 260/15 M X 3.767.449 10/1973 Hayashi et a1. 117/368 X 3,769.30] 10/1973 Hoover et L11. 117/362 X 3,772,052 11/1973 Kimura et al. 117/362 3,799.828 3/1974 Takashi et al. 156/229 Primary E,\'uminerGeorge F. Lesmes Assistant Examiner-Alan T. McDonald Attorney, Agent, or FirmPaul & Paul [57] ABSTRACT Color images having excellent resistances to sunlight. water and rubbing are developed by bringing, in accordance with the desired pattern, an acid-reactive colorless color forming dye solution in a non-volatile organic liquid capable of dissolving or swelling polystyrene into contact with an acid color developing high impact polystyrene sheet which comprises a substrate layer consisting of a high impact polystyrene film which has been stretched in at least one direction, at least one paper-like rough surface layer provided on the substrate layer by treating the surface portion of the high impact polystyrene film with an organic liquid capable of dissolving or swelling polystyrene. and having therein numerous microvoids, and acid color developing agent for the acid-reactive colorless color forming dye, the acid color developing agent being contained in the microvoids. whereby the colorless color forming dye solution penetrates into the microvoids and forms color images inside the sheet.

18 Claims, 5 Drawing Figures US. Patent Nov. 11, 1975 Sheet 1 013 3,919,450

US. Patent Nov. 11, 1975 Sheet2of3 3,919,450

U.S. Patent Nov. 11,1975 Sheet3of3 3,919,450

COLOR DEVELOPING HIGH IMPACT POLYSTYRENE SHEET AND METHOD OF DEVELOPING COLOR IMAGES INSIDE THE SAME The present invention relates to a color developing high impact polystyrene sheet capable of developing color images having excellent resistances to the rays of the sun, water and rubbing. anda method of developing the color images inside the sheet.

It is broadly known that acid reactive colorless color forming dyes, for example. Crystal violet lactone, leuco Auramine type compounds, leuco Methylene Blue type compounds and leuco Fluorane type'compounds can be developedby bringing them into contact with an acid color developing agent.

Such acid-reactive colorless color forming dyes and the acid color developing agents are utilized in the fields of duplicating and printing.

Generally, the conventional pressure sensitive no carbon copying paper is composed of a combination of a top sheet carrying, on a surface thereof, a layer of microcapsules containing therein a colorless color forming dye and a bottom sheet carrying, on a surface thereof, a layer of color developing agent effective for the colorless color forming dye. The color developing agent layer of the bottom sheet faces the microcapsule layer of the top sheet. i 1

The microcapsules are composed of fine particles of a solution of the colorless color forming dye in a nonvolatile solvent and a thin shells covering the fine particles. The thin shells are generally formed by a filmforming material. for example, gelatin."

When a pressure is applied onto the upper surface of the top sheet by hand-writing or type\vriting in accordance with the predetermined patternfthe microcapsules thus pressed are broken and the solution of the colorless color forming dye in the" broken microcapsules goes into contact with the color developing agent layer of the bottom sheet, so as to form colorimages on the bottom sheet.

The bottom sheet of the pressure-sensitive copying paper may be utilized asa printing sheet for printing with a printing ink containing the colorless color forming dye. That is, when colorless images formed by the colorless printing ink on the printing plate are brought into contact with the color developing agent layer of the printing sheet, the colorless printing ink images are transferred onto the surface of the Lcolor-developing layer of the printing sheet and color images are formed thereon. i I

The acid-reactive colorless color forming dyes are electron donors and theacid color developing agents are electron acceptors. Accordingly, when the colorless color forming dyes are brought into contactwith the color developing agent, anelectron of the colorless color forming dye molecule transfers to the color developing agentmolecule so as to convert the colorless dye to'color "dye."

The electron donor colorless dyes includes colorless triphenylmethane compounds, fore'xample, Crystal Vitional color developing sheet, the disadvantages as detailed below.

1. The triphenylmethane type coloring matters have an extremely low light fastness. That is, when exposed to the radiation of direct rays of the sun or ultraviolet ray for few hours, the color images of the triphenylmethane coloring matter are faded away and thereafter. disappear.

2. When wet with water, the color images of the triphenylmethane type coloring matter temporarily disappear.

ing or printing dye. In order to eliminate the above dis-.

advantages, it is desirable that the triphenylmethane type colorless .color forming dye is mixed with a leuco Methylene Blue type colorless color forming dye and the mixture is used as the duplicating or printing dye. I

Generally, the Methylene Blue type coloring matters have a high light fastness. However. it is also known that the Methylene Blue type coloring matters have the disadvantages of low color depth and high tendency to discoloration of the color images during storage over a long period of time. Accordinglygeven if the color images are formed by the coloring mixture of the triphenylmethane type coloring matter and the Methylene Blue type coloring matter. after fading away the color image of the triphenylmethane type coloring matter by the action of the rays of the sun. the remaining color images of the Methylene Blue type coloring matter are hard to read because of the low color depth thereof.

Additionally, during storage of the color. images of the mixture for a long period of time. the Methylene Blue type coloring matter images tend to discolor and. the refore, the color images are changed in color tone.

On the other hand. there are large disadvantages in the conventional color developing sheet for forming thereon color images. The color developing agents to be applied on the color developing sheet surface are electron acceptor compounds. For instance, the color 7 developing agent may be selected from inorganic acid solid materials, for example. attapulgite. bentonite. ka olin, zeolite and acid clay. These acid solid materials have a disadvantageous tendency to deteriorate and. therefore, to lose the capacity of developing the acidreactive colorless colorforming dyes when they are exposed to the atmosphere for more than about one month. While the basis of the deterioration of the acid solid materials is not quite clear, it is believed that the acid solidmaterials are deteriorated by absorbing water or reacting with carbon dioxide in atmosphere. From the above stated circumstances. it is clear that long storage of the color developing sheet carrying the inorganic acid solid material as the color developing agent. results in loss of practical usefulness thereof. I

Further. it is known that phenol, phenol derivatives and condensation products of phenol are useful as the color developing agent for the acid-reactive colorless color forming dyes. However, the phenolcompounds have the following defects.

1. High evaporation or sublimation property 2.,Readilyv deteriorated by the action of ultraviolet rays I a 3. High tendency to erode'the paper substrateof the color developing sheet. v 1

Accordingly, it is evident that the conventional color deveoping sheet carrying thereon the phenol com- 3 pound is not pertinent for storage for a long period of time.

Further. it is well known that the color images formed on the surface of the conventional color developing sheet have very small resistances against rubbing and water.

The object of the present invention is to provide a color developing high impact polystyrene sheet capable of maintaining brilliant color images developed from an acid reactive colorless color forming dye over a long period of time while protecting the color images from the actions of the rays of the sun and moisture.

Another object of the present invention is to provide a color developing high impact polystyrene sheet capable of developing colorless reactive of acid ractive col orless color forming dye to brilliant deep color images even after storage over a long period of time.

A further object of the present invention is to provide a method of developing color images having excellent resistances to the rays of the sun. water and rubbing. inside a color developing sheet.

The objects as stated above are accomplished by the color developing polystyrene sheet of the present invention which comprises a substrate layer consisting of a high impact polystyrene film which has been stretched in at least one direction. at least one rough surface layer provided on the surface of said substrate layer and having numerous microvoids formed therein. said rough surface layer being formed by treating the surface portion of the substrate film with a solvent capable of dissolving or swelling polystyrene. and an acid color developing agent contained in said microvoids. said acid color developing agent being effective for developing acid-reactive colorless color forming dyes.

It is known. from West German Pat. Application No. laid open No. 2.058.573. corresponding to US. Pat. No. 3.741.860 that a synthetic sheet having a paperlike rough surface available for writing. duplicating and printing with colored ink can be prepared from a high impact polystyrene film. Such high impact polystyrene sheet is produced by the process detailed below.

A polystyrene-rubber blend contains uniformly dispersed fine particles of an elastic organic polymer selected from natural rubber and synthetic rubbers. for example. styrenegrafted and non-grafted styrenebutadiene. polybutadiene. and acrylonitrile-butadienestyrene rubbers. Generally. the high impact polystyrene film comprises 80 to 98%. preferably. 92 to 96% by weight of polystyrene and 2 to preferably. 4 to 8% by weight of the rubber component as mentioned above. It is preferable that the fine rubber particles dispersed in the polystyrene have a mean size of about 1 to 7 1.. The polystyrene-rubber blend is shaped into a film or sheet by the conventional method. and the film or sheet is stretched in one or two directions. By the stretching. numerous fine particles of the rubber component dispersed in the polystyrene are elongated in one or more directions and fixed. in the elongated form. by the polystyrene component surrounding the rubber particles. Accordingly, the elongated and fixed rubber particles have a high potential for shrinkage.

When at least one surface portion of the stretched high impact polystyrene film is treated with an organic liquid capable of dissolving or swelling the polystyrene. and allowing the stretched rubber particles to rapidly shrink the rubber particles are released from the fixation and elongation. Accordingly. the released rubber particles rapidly shrink. The rapid shrinking of the rubher particles results in formation of microvoids in the treated portion of the film. And. the formation of the microvids causes the formation of a rough surface layer on the non-treated film portion. The microvoids thus formed contain the organic liquid. The organic liquid in the microvoids are removed by a conventional method. for example. evaporation. replacement with a non-solvent or washing.

The high impact polystyrene sheet thus treated has one or two opaque or translucent rough surface layers provided with numerous microvoids therein. It is preferable that the microvoids have a mean size of about 3 to 20p.

The opaque or translucent rough surface layer is capable of absorbing therewithin writing ink. duplicating ink or printing ink. Accordingly. the high impact polystyrene sheet thus treated has at least one color developing rough surface layer provided with numerous microvoids and a non-treated substrate layer. It is preferable that the non-treated substrate layer has a mean thickness of about 50% based on the thickness of the original high impact polystyrene film. The treated high impact polystyrene sheet can be utilized as the writing. duplicating and printing sheets.

The treating organic liquid for the high impact polystyrene may be selected from organic compounds capable of dissolving or swelling polystyrene.

That is. the organic liquid may be selected from aliphatic hydrocarbons. for example. n-hexane. n-heptane and n-octane.

As stated above. the rough surface layer formed by the treatment of the high impact polystyrene sheet includes therein numerous microvoids. In the color developing high impact polystyrene sheet of the present invention. the microvoids in the rough surface layer include therein an acid color developing agent effective for developing the acid-reactive colorless color forming dyes. Particularly. the acid color developing agent is deposited in the microvoids in the high impact polystyrene sheet in an amount of 0.5 to 3 g/m". and substantially confined therein.

The features of the present invention will be more apparent from the following description and the accompanying illustrative drawings of which:

FIG. 1 is a photograph showing the cross-sectional view of the color developing polystyrene sheet of the present invention.

FIGS. 2 through 5 are each a duplicating sheet including the color developing polystyrene sheet of the present invention.

In FIG. 1, a color developing polystyrene sheet 1 has a substrate layer 2 and rough surface layer 3 formed on both sides of the substrate layer 2. The rough surface layer 3 is provided with numerous microvoids formed therein and having a complicated and non-fixed configuration. These microvoids contain the acid color developing agent.

The acid color developing agent usable for the present invention has to be selected in consideration of the acid-reactive colorless color forming dye to be developed by the acid color developing agent. Generally, the acidreactive colorless color forming dye is selected from triphenylmethane type colorless color forming dyes, particularly. Crystal Violet lactone. Accordingly. the color developing agent may be selected from the compounds capable of electron-acceptance from the above-stated colorless color forming dyes and color developing them. For example. the color developing agent usable for the present invention may be selected from mono-carboxylic acids which may have one or more other radical than the carboxyl radical, for example, p-aminobenzoic acid, p-hydroxybenzoic acid and acetic acid; polycarboxylic acids which may have one or more other radical than the carboxyl radical, for example, succinic acid, maleic acid, citraconic acid, chloromaleic acid, itaconic acid, aconitic acid and phthalic acid; homopolymers of ethylenically unsaturated carboxylic acids. for example, polyacrylic acid and polymethacrylic acid; copolymersof ethylenically unsaturated acid anhydrides, for example, maleic, chloromaleic, citraconic, itaconic and aconitic acid anhydrides with at least one of ethylene and styrene; phenol compounds, for example, p-cumylphenol, p-phenylphenol p-tert-butylphenol. p-octylphenol and p-nonylphenol; polyphenol compounds, for" example, gallic acid, bis-phenol A, bis-phenol B and cathecol; novolak type condensation products of a phenol compound, for example, novolak type condensation products of phenol, p-phenylphenol, p-cumylphenol, 'p-tert-butylphenol, p-octylphenol and p-nonylphenol with formaldehyde, preferably, having at most 3 of phenol units; and phenol-acetylene polymers.

Since the acid color developing agent is confined inside the microvoids of the rough surface layer, it is substantially isolated from atmosphere and, therefore, can be protected from deterioration thereof by the action of moisture in the atmosphere or the rays of the sun.

The color developing high impact polystyrene sheet of the present invention may be prepared by the method as detailed below.

A high impact polystyrene film is stretched in one or more directions, preferably, two directions. The stretched film is treated with a solution of the acid color developing agent in an organic liquid capable of dissolving the acid color developing agent and of dissolving or swelling the polystyrene and allowing the stretched rubber particles to rapidly shrink.

The organic liquid may be selected from aliphatic hydrocarbons, for example, n-hexane, n-heptan and noctane.

The acid color developing agent may be selected from the compounds as stated hereinbefore.

The acid color developing agent may be dissolved direct into the organic solvent. Also, the acid color developing agent may be first dissolved into a solvent other than that to be used for dissolving or swelling the polystyrene, for instance, alcohols, for example, ethyl alcohol, n-butyl alcohol, ethers, ether, for example, tetrahydrofuran and 1,4-dioxane aliphatic hydrocarbons, for

' boxylic acids, for example, acetic acid and methacrylic acid; natural fat and oils, for example, linseed oil; and esters, for example, methyl formate and ethyl acetate. The first solution is mixed in a solvent for dissolving or swelling the polystyrene. Accordingly, the solvent for the polystyrene must be able to dissolve the acid color developing agent and the first solvent. When the high v impact polystyrene film is treated at its surface portion with the solution containing the acid color developing agent in the organic liquid, numerous microvoids are formed therein. The microvoids are impregnated with the solution. Thereafter, the organic solvent is removed so as to deposit the acid color developing agent inside the microvoids. After completely removing the organic solvent, the acid color developing agent is substantially confined within the microvoids.

" The above-stated method has an advantage that the proposed color developing high impact polystyrene sheet can be prepared by only one step from the high impact polystyrene film.

The color developing polystyrene sheet of the present invention may also be prepared by the method as detailed below.

The stretched high impact polystyrene film is treated at its surface portions with the solvent capable of dissolving or swelling the polystyrene, so as to obtain the high impact polystyrene sheet having rough surface layers wherein numerous microvoids are formed. The rough surface layer is treated with a solution of the acid color developing agent in a solvent. This solvent may be selected from aliphatic hydrocarbons, for example n-heptane and n-octane; aromatic hydrocarbons. for example, toluene and xylene; ethers, for example, ethyl ether and 1,4-dioxane; ether alcohols, for example, B hydroxyethyl methyl ether and B-hydroxyethyl ether; carboxylic acids, for example, acetic acid and methacrylic acid; ketones, for example. acetone and methylisobutyl ketone; esters, for example. ethyl acetate and methyl formate; halogenated hydrocarbons, for example, tetrachloroethane; alcohols, for example. methyl alcohol and ethyl alcohol; and mixtures of two or more of the abovestated compounds. When applied onto the rough surface of the sheet, the solution of the acid color developing agent penetrates into the microvoids and is contained therein. By. removing the solvent, the ac'id color developing agent is deposited in the microvoids, and after completely removing the solvent, the acid color developing agent is substantially eonfined in the microvoids. This method has the advantages that the high impact polystyrene sheet having the rough surface layer whichhas been provided already can be utilized at will for the preparation of the colordeveloping sheet, and that the color developing agent can be applied onto any one surface layer of the sheet at will. I

Even if the color developing high impact polystyrene sheet of the present invention is prepared by any one of the methods stated above. it is preferable that the microvoids have a mean size of about 3 to 20,11, and that the non-treated substrate layer has a mean thickness of about 50% based on that of the originalfilm.

In order to develop the acid-reactive colorless color forming dye on the developing sheet, the colorless color forming dye should be transferred onto the rough surface layer of the developing sheet in accordance with the predetermined pattern.

The present invention includes a method of developing color images from an acid-reactive colorless color forming dye, inside the color developing high impact polystyrene sheet of the present invention. In the method of the present invention, a solution or ink containing an acid-reactive colorless color forming dye selected from leuco triphenylmethane type and leuco Fluorane type colorless color forming dyes is transferred onto the rough surface of the color developing sheet in accordance with the predetermined pattern.

The colorless color forming dyes are generally dissolved in an organic solvent selected from non-volatile liquids such as vegetable oils. for example, olive oil, castor oil. cotton seed oil and peanut oil; mineral oils, for example, various paraffin oils; synthetic oil, for example, chlorinated diphenyls, alkyl diphenyls. alkyl naphthalenes, aryl alkanes. chlorinated paraffins, dioctyl phthalate and tricresyl phosphate, and mixtures of two or more of the above-mentioned oils. These solvents can sufficiently wet and dissolve or swell the poly styrene forming the color developing sheet. Therefore. when the solution of the colorless color forming dye is applied onto the rough surface layer of the color developing sheet. the solution can rapidly penetrate into the microvoids containing the acid color developing agent therewithin while dissolving or swelling the polystyrene. By the above-stated procedure. the colorless color forming dye in the solution is brought into contact with the acid color developing agent in the microvoids. and converted to the coloring matter so as to form color images. The solution containing the coloring matter thus developed further penetrates to the bottom portion of the rough surface layer. or sometimes to the substrate layer, and is fixed there in such a condition that the coloring matter is mixed with the polysty rene dissolved in the solvent.

As stated above, the color images thus formed are absorbs the light radiated to the sheet and protects the color images from the radiation of light. Accordingly, even if the color images are formed by the triphenylmethane type dye which has essentially very low light fastness. the color images embedded in the high impact polystyrene sheet show an unexpected high light fastness.

The color developing high impact polystyrene sheet of the present invention may be utilized as a bottom sheet of a pressure sensitive no carbon duplicating sheet.

Referring to FIG. 2, a no carbon duplicating sheet 21 is composed of a top sheet 22 and a bottom sheet 23. The top sheet 22 comprises a base sheet 24 consisting of paper and a microcapsule layer 25 applied onto the lower surface of the base sheet 24 and consisting of numerous microcapsules and a binder incorporating the microcapsules into one layer. The bottom sheet 23 is made of a color developing high impact polystyrene sheet of the present invention which comprises a substrate layer 26 and a color developing rough surface layer 27 facing the microcapsule layer 25.

When the no carbon duplicating sheet 21 is pressed on the upper surface of the top sheet 22 in accordance with the predetermined pattern. the microcapsules of the top sheet 22 are broken by the pressure in accordance with the pattern. The duplicating ink flowed out from the broken microcapsules penetrates into the color developing rough surface layer of bottom sheet 23 while dissolving or swelling polystyrene thereof and contacts the color developing agent contained in the microvoids. Accordingly, the color images of the desired pattern are formed inside the rough surface layer 27 of the bottom sheet 23.

Referring to FIG. 3, a no carbon duplicating sheet 30 is composed of a top sheet 31. an intermediate sheet 32 and a bottom sheet 33.

The top sheet 31 is composed ofa base sheet 34 consisting of paper and a microcapsule layer 35 provided on the upper surface of the base sheet 34. The interme diate sheet 32 is composed of a color developing high impact polystyrene sheet of the present invention having a substrate layer 36 and color developing rough surface layer 373 provided on the upper side of the substrate layer 36 and facing the microcapsule layer 35 of the top sheet 31, and a microcapsule layer 38 provided on the lower side of the substrate layer 36. The bottom sheet 33 is made ofa color developing high impact polystyrene sheet of the present invention which has a substrate layer 39 and a color developing rough surface layer 37b provided on the upper side of the substrate layer 39 and facing the microcapsule layer 38 of the intermediate sheet 32.

When the duplicating sheet 30 is pressed on the upper surface of the top sheet 31 in accordance with the predetermined pattern, color images of the pattern are formed within the rough surface layers 37a and 37b of the intermediate and bottom sheets 32 and 33.

The duplicating sheet may comprise two or more intermediate sheets as stated above. The bottom and intermediate sheets carrying color images are separated from the top sheet and utilized as open air display sheets, labels and copying sheets to be kept over a long period of time.

Referring to FIG. 4, a pressure sensitive no carbon duplicating sheet 41 is composed of a top sheet 42 and a bottom sheet 43.

The top sheet 42 consists of a base sheet 44 made of a paper or synthetic polymer. and a microcapsule layer 45 provided on the lower surface of the base sheet 44. The bottom sheet 43 is composed of an adhesive duplicating sheet 46 and a releasable sheet 47 capable of being separated from the adhesive duplicating sheet 46. The adhesive duplicating sheet 46 is composed of a color developing high impact polystyrene sheet 48 of the present invention which has a substrate layer 49 and a color developing rough surface layer 50, facing the microcapsule layer 45 of the top sheet 42, and an adhesive layer 51 provided on the lower surface of the high impact polystyrene sheet 48. The releasable sheet 47 is composed of a base sheet 52 made of paper or a synthetic polymer sheet and a layer 53 of releasing material facing the adhesive layer 51 of the duplicating sheet 46 and being adhered to the adhesive layer 51 at such a very small adhesiveness that the releasable sheet 47 can be easily separated from the duplicating sheet 46.

After forming the desired color images within the rough surface layer of the duplicating sheet 46 in accordance with the predetermined pattern, the releasable sheet 47 is separated from the duplicating sheet 46 and the duplicating sheet 46 carrying the desired color images is adhered to a desired article or material through the adhesive layer 51.

Referring to FIG. 5, a no carbon duplicating sheet is composed of a top sheet 61, an intermediate sheet 62 and bottom sheet 63. The top sheet 61 is composed of a base sheet 64 made of paper or a synthetic polymer film and a microcapsule layer 65 provided on the lower surface of the base sheet 64. The intermediate sheet 62 is composed of an adhesive duplicating sheet 66 and a releasable sheet 67. The adhesive duplicating sheet 66 consists of a color developing high impact polystyrene sheet 68 having a substrate layer 69 and a color developing rough surface layer 70 facing the microcapsule layer 65 of the top sheet 61, and an adhesive layer 71 provided on the lower surface of the high impact polystyrene sheet 68. The releasable sheet 67 consists of a base sheet 72 made of paper or a synthetic polymer sheet, and a layer 73 of a releasing agent provided on the upper surface of the base sheet 72, and a microcapsule layer 74 provided on the lower surface of the base sheet 72. The releasing agent layer 73 adheres to the adhesive layer 71 of the duplicating sheet'66 with a very small adhesive strength and, therefore, is easily peeled off from the adhesive layer 71. The bottom sheet 63 consists of a color developing high impact polystyrene sheet of the present invention having a substrate layer 75 and a color developing rough surface layer 76 facing the microcapsule layer 74 of the intermediate layer 62.

After duplicating, the duplicating sheet 66 of the intermediate sheet 62 is separated from the releasable sheet 67 and adhered to a desired article or material, and the bottom sheet 63 is kept as a record. Needless to say, two or more intermediate sheets, the same as in FIG. 5, may be inserted between the top and bottom sheets.

The color developing high impact polystyrene sheet of the present invention possesses the advantages detailed below.

1. Even if the colorless color forming dye having a low resistance to water and a poor light fastness, such as triphenylmethane type colorless dyes, is used, the color images formed on the color developing sheet of the present invention have an excellent light fastness and resistance to water. Therefore, the triphenylmethane type colorless dye does not need to be mixed with the Methylene Blue type colorless dye which has been conventionally used to enhance the light fastness of the I color images formed by the triphenylmethane type dye. This is effective to lower the color image formingcost and eliminate the problem that the Methylene Blue type coloring matter readily discolors during storage.

If the Methylene Blue type colorless dye is used in the form of mixture with the triphenylmethane type colorless dye, it is necessary to dissolve the Methylene Blue type colorless dye in a strong non-volatile solvent such as polychlorobenzenes which has a high toxicity, because of the difficulty of dissolving it. However, since the color developing sheet of the present invention does not need the Methylene Blue type colorless dye mixed with the triphenylmethane type colorless dye, there is the advantage that the solvent to be used to dissolve the colorless dye is non-toxic.

2. Even if the color developing sheet is stored for a .long period of time, the activity of the color developing agent in the surface layer of the sheet practically does not change because the color developing agent is contained in the closed microvoids and protected from the actions of moisture in atmosphere, Compared with this, the conventional color developing papers are changed in during storage of 1 to several months quality and the color developing activity is lowered or disappeared. Accordingly, it is obvious that the color developing sheet of the present invention has a larger advantage in practical use than that of the conventional color developing paper. 7

3. Even though the color developing sheet; of the present invention is moistened with water or exposed to the rays of the sun or ultraviolet rays, there is no change in the activity of the color developing agent therein. I

4. Since the color developing agent. is substantially, 5 confined in the closed microvoids, the,color developing agent may be a volatile or sublimatable solid or liquid.

5. The color developing sheet of the present invention can be utilized as a recording sheet to be kept over a long period of time, because the color image developed on the color developing sheet has an excellent light fastness and resistances to water and rubbing.

6 The color developing sheet of the present invention can be utilized as an indicating sheet to be used in the open air or chit sheet for delivery without cover sheet. Compared with this, the indicating sheet and the chit sheet carrying color images developed on the conventional color developing sheet need to be covered by a clear film, because the color images have a poor light fastness and low resistance to water.

7. Since the color developing agent is contained in the microvoids, there is no increase of the thickness of the sheet by incorporation with the color developing agent. In the conventional color .dcveloping sheet, a surface layer containing the color developing agent is attached on the surface of the substrate paper. This attaching results in an increase of thickness of the sheet.

Accordingly, the present invention can provide a very thin color developing sheet which is effective to obtain clear color images on a plurality of color developing sheets even if they are simultaneously superimposed and subjected to duplication.

8. The color developing sheet used as a printing sheet for the conventional printing processes. for example. typographic, lithographic and intaglio printings. has the following advantages. Since the printing ink penetrates into the inside of the sheet, the printed sheets do not adhere to each other. Further, since the color images are formed inside the sheet, the color images have a very high resistance to abrasion.

The present invention will be further illustrated by the following examples which are given by way of illustration and not as limitations of the scope of the present invention. In the examples all parts and percentages are by weight unless otherwise stated.

EXAMPLE 1 A. Preparation of top sheet A mixture of 2 g of gelatin and 2 g of gum arabic was dissolved in 1 litre of pure water, and the solution was adjusted to a pH of 10.0 by adding 10% sodium hydroxide aqueous solution. To the solution was added 20 g of a dye solution which has been prepared by dissolving 6 parts of Crystal Violet lacton in 100 parts of hexylnaph- ,lthalene. The mixture was emulsifiedby using a homogenizer at a temperature of C. The emulsion was adjusted to a pH of 4.0 by adding 10% acetic acid. After cooling the emulsion to a temperature of 10C, 2 g of an aqueous solution of at least 37% formaldehyde was added to the emulsion. The solution was adjusted to a pH of 10.0 by adding 10% aqueous solution of sodium hydroxide. The resultant emulsion was left to stand over a day and night and then concentrated. After completing the concentraton step, numerous microcapsules containing a colorless dye solution were obtained. 100

1 1 parts of the microcapsules were mixed with an aqueous solution containing as a binder. 10 parts of starch. The mixture was applied to a surface of a paper and dried to prepare the top sheet.

B. Preparation of bottom sheet 250 g of a commercial 2.2'-methylene-bis(4-chlorophenol) was dissolved in a uniform mixture of4.9 litres of n-heptane and 0.1 litre of ,B-hydroxyethyl ether while heating. and the solution was maintained at a temperature of 50C. A stretched high impact polystyrene film of a thickness of 100 p. was immersed in the solution for 2 seconds and dried in the atmosphere A polystyrene sheet having both upper and lower rough surfaces was obtained. The thickness of the resultant sheet was 120 The rough surfaces were provided with numerous microvoids containing therein the 2.Z'-methylene-bis(4- chlorophenol) as a color developing agent. and a mean size of about 5 [.L.

C. Preparation of pressure sensitive no carbon duplicating sheet The top sheet prepared above was superimposed on the bottom sheet prepared above in such a manner that the microcapsule layer of the top sheet faced the rough surface of the bottom sheet. to prepare a set of no carbon duplicating sheets.

D. Duplicating Predetermined images were hand written on the top sheet of the no carbon duplicating sheets prepared above. Brilliant violet blue images were formed on the bottom sheet.

E. Testing of the color images obtained above The rough surface of the bottom sheet carrying the color images was exposed to the direct rays of the sun for 8 hours. A ratio in percent of depth of the color images after exposure with respect to that before exposure was determined. The ratio stated above showed the light fastness of the color images. One rough surface of the bottom sheet before the duplication was exposed to the direct rays of the sun for 4 hours. The duplication was effected onto the exposed rough surface of the bottom sheet. A ratio in percent of depth of the color images formed on the exposed surface layer with respect to that on the non-exposed surface layer of the bottom sheet. was determined. The ratio indicated the light fastness of the color developing agent contained in the bottom sheet.

For comparison. two conventional bottom sheets were prepared using combinations of 1) paper and acid clay and. (2) paper and novolak phenol resin.

The light fastnesses of the color images and color developing agent on the bottom sheet of the present invention and the conventional bottom sheets (1) and (2). are shown in Table 1.

Table 1 Bottom sheet Bottom The The sheet of conventional comentional bottom sheet (ll) bottom sheet (I) Example Item 1 Light fastness of agent applied to bottom sheet Example bottom sheet (Ill Item I (ll bottom sheet ('1' J Table 1 clearly shows that the color image and the color developing agent in the bottom sheet of the present invention have a remarkably higher light fastness than those of the conventional bottom sheets (I) and (II).

The color images formed on the bottom sheet of the present invention did not run or flow away even when immersed in water. The rough surface carrying the color images of the bottom sheet of the present invention was moistened and rubbed. However. the color images did not bleed. Compared with this. when the conventional bottom sheet (I) was immersed in water. the color images thereon rapidly ran. Also. when the conventional bottom sheets (I) and (II) were moistened and rubbed. the color images thereon did bleed and dis appear.

EXAMPLE 2 The same procedures as in Example 1 were repeated except for the following items.

A. Preparation of color developing agent A mixture of 170 parts of p-phenylphenol. parts of 37% aqueous solution of formaldehyde. 1 part of oxalic acid anhydride and 50 parts of 77 aqueous solution of hydrochloric acid. was charged into a flask with a reflux condenser. and heated at the boiling point thereof to react them. After 4 to 6 hours the heating was stopped. and water in the mixture was removed. The resultant product had a molecular weight of 270 to 400. The flask was reduced in pressure by using an aspirator and. thereafter. the product was distilled under the reduced pressure at a temperature of 100C. The resultant product had a melting point of l00C.

B. Preparation of bottom sheet g of the product as prepared above were dissolved as a color developing agent. in 1 litre of B- hydroxyethyl ether. the solution was uniformly mixed with 4 litres of n-octane. raised to a temperature of 50C. and maintained at this temperature. A high impact polystyrene film of a thickness of I00 p. which had been stretched in two directions was immersed in the mixture solution for 5 seconds and thereafter, immediately airdried to remove the solvent. A sheet having both an upper and lower rough surface layer was obtained. The sheet contained the color developing agent consisting of a condensation product of p-phenylphenol with formaldehyde within the microvoids formed in the rough surface layer and. therefore. was usable for the bottom sheet of the pressure sensitive no carbon duplicating sheet. The thickness of the resultant sheet was ,a.

C. Preparation of duplicating sheet A pressure sensitive no carbon duplicating sheet was prepared by superimposing the same top sheet as in Ex ample l on the bottom sheet prepared above.

D. Duplicating Predetermined letters were typewritten on the top sheet of the duplicating sheet. Brilliant violet blue images were formed in the rough surface layer of the bottom sheet facing the microcapsule layer of the top sheet.

E. Testing of color images The light fasteness of the color images formed on the bottom sheet was determined by the same method as in Example 1.

The light fastness of the color developing agent contained in the bottom sheet was determined by exposing it, using a xenon type fading meter. for "hours and duplicating in the same manner as in Example 1. For comparison the same tests as stated above were applied to the same conventional bottom sheets (1) and (11) as used in Example 1. The results of the tests are shown in bottom sheet ()2 From Table 2. it is obvious that the color images and the color developing agent in the bottom sheet of the present invention had a remarkably higher light fastness than those of the conventional bottom sheets. Further, it was observedthat the color images formed in the bottom sheet of the present invention had a remarkably higher resistance to water and rubbing than those of the conventional bottom sheets.

EXAMPLE 3 The same procedures as in Example 1 were repeated except for the following changes.

A. Color developing agent A commercial p-aminobenzoic. acid was used as the color developing agent.

B. Preparation of bottom sheet A high impact polystyrene sheet of 100 ,u. thickness whichhas been stretched in two directions, was im-, mersed in n-heptane at a temperature of 50C for 30 seconds, and thereafter, immediately dried in, atmo-- sphere to remove the n-heptane. A paper-like high impact polystyrene sheet having both upper and lower rough surface layers was obtained. The thickness of the resultant sheet was about 145 p. 100 g of p-aminobenzoic acid was dissolved in 1 litre of: B-hydroxymethyl ethyl ether. and into the solution was mixed 0.1 litre of Xylene. The mixture solution was applied to one surface of the polystyrene sheet prepared above. The resultant sheet had a surface layer provided with numerous microvoids containing therein the color developing agent and, therefore. usable for the bottom sheet of the noncarbon duplicating sheet.

C. Preparation of duplicating sheet The same top sheet as used in Example 1 was superposed on the bottom sheet prepared above to prepare a pressure sensitive no carbon duplicating sheet.

D. Duplicating Predetermined letters were hand written on the top sheet of the above-mentioned duplicating sheet. Brilliant violet blue images were formed in the rough surface layer of thebottom sheet.

E. Testing of color images The'ligh t fastness of the color images formed in the bottom sheet was tested in the same manner as in Example I. Also. the light fastness of the color developing agent contained in the bottom sheet was determined in the same manner as in Example 1. For comparison. the same conventional bottom sheets l and (2) as used in Example 1 were put under the same top sheets used in Example 1. and the same procedures were repeated for the conventional duplicating sheets 1 and (2) prepared above.

The results of testings are shown in Table 3.

Table 3 Bottom sheet Bottom sheet of Comparison Comparison Example Example [Example Item 3 (ll (ll) Light fastness of color image (f l )3 15 3t) Light fastness of color developing agent applied to 81 4t) 51 bottom sheet ("2 In view of Table 3. it is evident that the color images and color developing agent contained in the bottom sheet of the present invention. have a remarkably higher light fastness than those of the comparison bottom sheet. Further. it was observed that the color images formed in the bottom sheet of the present invention have, a remarkably higher resistances to water and rubbing than those of the conventional bottom sheets.

EXAMPLE 4 The same bottom sheet as in Example 1 was used as a printing sheet. Predetermined images of a printing colorless-ink consisting of 5% of Rhodamine B lactam 40% of volume pigment. of varnish and 25% of diarylethane. were printed on the rough surface of the printing sheet (25 -cm) using a typographic printing' testing machine. The colorless ink rapidly penetrated'into the rough layer and brilliantred images were immediately formed therein. Even after superimposing the printed sheets over a week under a weight of 10 kg/cm there was no adhering of the sheets to each other. v

' The color images thus formed had excellent high fastness and resistance to water and rubbing.

v I EXAMPLE 5 The same bottom sheets as prepared in Example 2 were used as printing sheets for offset printing.

The images of the same colorless ink as in Example 4 was printed on 500 printing sheets under a printing pressure of about l2 kg/cm using a rotary offset press at a velocity of 120 sheets/minute.

The printing ink was absorbed immediately by the rough surface layer of the printing sheet and brilliant blue images were formed therein. No blocking of the printed sheet was observed. The light fastness of the color images was determined by exposing them for 24 hours to artificial light of a fading meter. The color im ages were faded by an amount of 5%. For comparison. 500 pieces of the conventional printing sheets (25 X cm) were prepared by the following method. A mixture of I00 parts of the same color developing agent as that used above. which was finely crushed by a ball mill. 40 parts of acid clay. 20 parts of a latex of styrene butadien rubber and 1 part of a dispersing agent. was uniformly agitated in a homomixer. The mixture was applied on the surface of paper in a weight of c g/m'-'. and dried.

The same printings as stated above were applied to the comparison printing sheets under a pressure of twice that for the printing sheets of the present example. The same fading testing as stated above was ap plied to the color images. The color images were faded in an amount of From the above description. it is clear that the color images formed in the printing sheet of the present invention have an excellent light fastness.

what we claim is:

l. A color developing high impact polystyrene sheet comprising:

l. a substrate layer consisting essentially of a high impact polystyrene film which has fine particles of a rubber component uniformly dispersed in the polystyrene and which has been stretched in at least one direction.

". at least one paper-like rough surface layer provided on said substrate layer and having therewithin numerous microvoids. said microvoids being formed by treating the surface portion of the high impact polystyrene film with an organic liquid capable of dissolving or swelling the polystyrene and capable of allowing the stretched particles of said rubber component to rapdily shrink. and

3. an acid color developing agent contained in said microvoids. said acid color developing agent being capable of developing acid-reactive colorless color forming dye.

2. A color developing sheet as claimed in claim 1. wherein said acid color developing agent is selected from the group consisting of monocarboxylic acids. polycarboxylic acids. homopolymers and copolymers of ethylenically unsaturated carboxylic acids. phenol compounds. polyphenol compounds. condensation products of a phenol compound and formaldehyde. phenol-acetylene polymers. p-hydroxystyrene polymer. organic sulfonic acids and its polymers and boric acid.

3. A color developing sheet as claimed in claim 2, wherein said monocarboxylic acid is selected from the group consisting of p-aminobenzoic acid. p-hydroxybenzoic acid and acetic acid.

4. A color developing sheet as claimed in claim 2, wherein said polycarboxylic acid is selected from the group consisting of succinic acid. maleic acid. citra- 16 conic acid. chloromaleic acid. itaconic acid. aconitic acid and phthalic acid.

5. A color developing sheet as claimed in claim 2. wherein said homopolymer of ethylenically unsaturated carboxylic acid is selected from the group consisting of polyacrylic acid and polymethacrylic acid.

6. A color developing sheet as claimed in claim 2. wherein said copolymer of ethylenically unsaturated carboxylic acid anhydride is selected from the group consisting of copolymers of maleic. chloromaleic. citraconic. itaconic and aconitic acid anhydrides with at least one of ethylene and styrene.

7. A color developing sheet as claimed in claim 2. wherein said phenol compound is selected from the group consisting of phenol. pcumylphenol. p-phenylphenol. ptert-butylphenol. p-octylphenol and p-nonylphenol.

8. A color developing sheet as claimed in claim 2. wherein said polyphenol is selected from the group consisting of gallic acid. bis-phenol A. bis-phenol B and cathecol.

9. A color developing sheet as claimed in claim 2, wherein said novolak type condensation product of a phenol compound is selected from the group consisting of novolak type condensation products of phenol. pphenylphenol. p-cumylphenol. p-tert-butylphenol. poctylphenol and p-nonylphenol with formaldehyde. each having 3 or less phenolic components.

10. A color developing sheet as claimed in claim 1. wherein said high impact polystyrene film comprises to 98% by weight of polystyrene and 2 20% by Weight of a rubber component selected from the group consisting of styrenegrafted and non-grafted polybutadiene. styrene-butadiene rubber and acrylonitrile-butadienestyrene rubbers. and natural rubber.

11. A color developing sheet as claimed in claim 1, wherein said acid color developing agent in the high impact polystyrene sheet is in an amount of 0.5 3 g/m 2 12. A color developing sheet as claimed in claim 1 wherein said rubber component is selected from the group consisting of natural rubber. and styrene-grafted and non-grafted styrene-butadiene. poly-butadiene and acrylonitrite-butadiene-sytrene rubbers.

IS. A color developing sheet as claimed in claim 1, wherein said high impact polystyrene film comprises from about 80 to 98 per cent by weight of the polystyrene and from about 2 to 20 per cent by weight of the rubber component.

14. A color developing sheet as claimed in claim I, wherein said particles of said rubber componenet have a size from 1 to 7 microns.

15. A color developing sheet as claimed in claim 1, wherein said organic liquid is an aliphatic hydrocarbon.

16. A color developing sheet as claimed in claim 15, said aliphatic hydrocarbon being selected from the group consisting of n-hexane. n-heptane and n-octane.

17. A color developing sheet as claimed in claim 1, wherein said microvoids have a size within the range of from about 3 to 20 a.

18. A color developing sheet as claimed in claim 1, wherein said substrate layer has a mean thickness of about 50 per cent based on that of the original film.

l =l l l 

1. A COLOR DEVELOPING HIGH IMPACT POLYSTYRENE SHEET COMPRISING:
 1. A SUBSTRATE LAYER CONSISTING ESSENTIALLY OF A HIGH IMPACT POLYSTYENE FILM WHICH HAS FINE PARTICLES OF A RUBBER COMPONENT UNIFORMLY DISPERSED IN THE POLYSTYRENE AND WHICH HAS BEEN STRETCHED IN AT LEAST ONE DIRECTION,
 2. AT LEAST ONE PAPER-LIKE ROUGH SURFACE LAYER PROVIDED ON SAID SUBSTRATE LAYER AND HAVING THEREWITHIN NUMEROUS MICROVIODS, SAID MICROVOIDS BEING FORMED BY TREATING THE
 2. at least one paper-like rough surface layer provided on said substrate layer and having therewithin numerous microvoids, said microvoids being formed by treating the surface portion of the high impact polystyrene film with an organic liquid capable of dissolving or swelling the polystyrene and capable of allowing the stretched particles of said rubber component to rapdily shrink, and
 2. A color developing sheet as claimed in claim 1, wherein said acid color developing agent is selected from the group consisting of monocarboxylic acids, polycarboxylic acids, homopolymers and copolymers of ethylenically unsaturated carboxylic acids, phenol compounds, polyphenol compounds, condensation products of a phenol compound and formaldehyde, phenol-acetylene polymers, p-hydroxystyrene polymer, organic sulfonic acids and its polymers and boric acid.
 3. A color developing sheet as claimed in claim 2, wherein said monocarboxylic acid is selected from the group consisting of p-aminobenzoic acid, p-hydroxybenzoic acid and acetic acid.
 3. an acid color developing agent contained in said microvoids, said acid color developing agent being capable of developing acid-reactive colorless color forming dye.
 3. AN ACID COLOR DEVELOPING AGENT CONTAINED IN SAID MICROVOIDS, SAID ACID COLOR DEVELOPING AGENT BEING CAPABLE OF DEVELOPING ACID-REACTIVE COLORLESS COLOR FORMING DYE.
 4. A color developing sheet as claimed in claim 2, wherein said polycarboxylic acid is selected from the group consisting of succinic acid, maleic acid, citraconic acid, chloromaleic acid, itaconic acid, aconitic acid and phthalic acid.
 5. A color developing sheet as claimed in claim 2, wherein said homopolymer of ethylenically unsaturated carboxylic acid is selected from the group consisting of polyacrylic acid and polymethacrylic acid.
 6. A color developing sheet as claimed in claim 2, wherein said copolymer of ethylenically unsaturated carboxylic acid anhydride is selected from the group consisting of copolymers of maleic, chloromaleic, citraconic, itaconic and aconitic acid anhydrides with at least one of ethylene and styrene.
 7. A color developing sheet as claimed in claim 2, wherein said phenol compound is selected from the group consisting of phenol, p-cumylphenol, p-phenylphenol, p-tert-butylphenol, p-octylphenol and p-nonylphenol.
 8. A color developing sheet as claimed in claim 2, wherein said polyphenol is selected from the group consisting of gallic acid, bis-phenol A, bis-phenol B and cathecol.
 9. A color developing sheet as claimed in claim 2, wherein said novolak type condensation product of a phenol compound is selected from the group consisting of novolak type condensation products of phenol, p-phenylphenol, p-cumylphenol, p-tert-butylphenol, p-octylphenol and p-nonylphenol with formaldehyde, each having 3 or less phenolic components.
 10. A color developing sheet as claimed in claim 1, wherein said high impact polystyrene film comprises 80 to 98% by weight of polystyrene and 2 - 20% by weight of a rubber component selected from the group consisting of styrenegrafted and non-grafted polybutadiene, styrene-butadiene rubber and acrylonitrile-butadiene-styrene rubbers, and natural rubber.
 11. A color developing sheet as claimed in claim 1, wherein said acid color developing agent in the high impact polystyrene sheet is in an amount of 0.5 - 3 g/m2. 2 .
 12. A color developing sheet as claimed in claim 1 wherein said rubber component is selected from the group consisting of natural rubber, and styrene-grafted and non-grafted styrene-butadiene, poly-butadiene and acrylonitrite-butadiene-sytrene rubbers.
 13. A color developing sheet as claimed in claim 1, wherein said high impact polystyrene film comprises from about 80 to 98 per cent by weight of the polystyrene and from about 2 to 20 per cent by weight of the rubber component.
 14. A color developing sheet as claimed in claim 1, wherein said particles of said rubber componenet have a size from 1 to 7 microns.
 15. A color developing sheet as claimed in claim 1, wherein said organic liquid is an aliphatic hydrocarbon.
 16. A color developing sheet as claimed in claim 15, said aliphatic hydrocarbon being selected from the group consisting of n-hexane, n-heptane and n-octane.
 17. A color developing sheet as claimed in claim 1, wherein said microvoids have a size within the range of from about 3 to 20 Mu .
 18. A color developing sheet as claimed in claim 1, wherein said substrate layer has a mean thickness of about 50 per cent based on that of the original film. 